This tab covers the external male genitalia — the erectile bodies and fascial layers of the penis, its arterial supply, venous drainage and innervation, and the layered scrotum and spermatic cord.
Penis: Structure and Erectile Bodies
On stretch, the superior surface is the dorsum and the inferior the ventrum. The layers surrounding the corpora, superficial to deep, are: skin, dartos (continuous with Scarpa's and Colles' fasciae), tela subfascialis, Buck's fascia, and tunica albuginea.
- Corpora cavernosa — paired erectile cylinders within the tunica albuginea (separated from it by the space of Smith); their crura attach to the puboischial rami. A permeable septum allows free vascular communication. In the flaccid state the sinusoids hold venous-level blood gases; in erection rapid arterial inflow shifts these to arterial levels.
- Corpus spongiosum — carries the urethra (its proximal dilation is the bulb) and expands distally as the glans. It lacks the outer longitudinal tunica layer and intracorporeal struts, keeping it a low-pressure structure during erection.
- Tunica albuginea — a bilayered (inner circular, outer longitudinal) type I collagen sheath. The outer longitudinal layer is absent on the ventral groove (5–7 o'clock) — the weakest point where most prostheses extrude, and a factor in the dorsal curvature of Peyronie's disease (60–70% of plaques are dorsal).
- Buck's fascia lies external to the tunica; the paired dorsal arteries, paired dorsal nerves, and (single) deep dorsal vein lie deep to it, while the superficial dorsal vein lies external to it. A penile fracture (tear of the tunica albuginea) produces a hematoma contained by Buck's fascia. Support comes from the fundiform ligament (from Colles fascia) and the suspensory ligament (from Buck's fascia). The only penile glands are the smegma-producing glands of Tyson at the corona.
Penis: Vasculature
- Deep arterial system — the internal pudendal artery becomes the common penile artery, which gives three branches (CBD): Cavernosal (helicine arteries → tumescence of the corpus cavernosum), Bulbourethral (corpus spongiosum, urethra, glans), and Dorsal (responsible for glans engorgement during erection, plus distal shaft skin). Cavernosal and dorsal branches are protected by a periarterial sheath from occlusion by the tunica during erection. Accessory pudendal arteries (often from the obturator) may be the dominant cavernosal supply.
- Superficial arterial system — branches of the external pudendal artery (from the femoral) supply the penile skin via the dartos; this supply is independent of the erectile bodies, making penile skin ideal for pedicled mobilisation.
- Venous drainage — emissary veins drain into the deep dorsal vein (main drainage of the glans and distal two-thirds of the corpora cavernosa; beneath Buck's fascia, between the paired dorsal arteries) → periprostatic plexus → internal iliac vein. The superficial dorsal vein (external to Buck's fascia) drains into the saphenous vein.
- Lymphatics — the penile shaft drains to both the superficial and deep inguinal nodes.
Penis: Innervation
- Somatic — the paired dorsal nerves of the penis (the first branch of the pudendal nerve, S2–S4) run along the dorsum and supply sensation to the glans; the penile skin is supplied by the genitofemoral nerve.
- Autonomic — the paired cavernous nerves (S2–S4) arise from the pelvic plexus, run posterolateral to the prostate as the neurovascular bundle (the landmark for nerve-sparing prostatectomy), and innervate the corpus cavernosum and penile urethra.
Scrotum and Spermatic Cord
The median raphe runs from the meatus to the anus; no scrotal vessels, lymphatics, or nerves cross it. The scrotal layers (superficial to deep) mirror the abdominal wall: skin, dartos, external spermatic fascia, cremaster, internal spermatic fascia, tunica vaginalis, tunica albuginea, tunica vasculosa, testis — with dartos from Scarpa's fascia, external spermatic fascia from the external oblique, cremaster from the internal oblique, and internal spermatic fascia from the transversalis fascia. The gubernaculum fixes the testis at its lower pole; absence of the gubernaculum and testicular mesentery is the Bell-Clapper deformity, predisposing to torsion.
- Vasculature — the external pudendal arteries supply the anterior scrotal wall (perineal branches the posterior); because the testes and spermatic fasciae have a separate blood supply, only skin and dartos are debrided in Fournier gangrene.
- Innervation — anterior wall: ilioinguinal (L1) and the genital branch of the genitofemoral (L1–L2); posterior wall: perineal and posterior femoral cutaneous (S3) nerves.
- Spermatic cord contents — the vas deferens (posteriorly), the testicular, deferential, and cremasteric arteries, the pampiniform plexus, lymphatics, and the genital branch of the genitofemoral nerve. The ilioinguinal nerve runs outside the cord (in the cremaster layer) and can be spared without individual dissection.
Self-Test
1. Why does the corpus spongiosum lack rigidity during erection? It lacks the outer longitudinal layer of the tunica albuginea (and intracorporeal struts), so it remains a low-pressure structure.
2. What is the relationship of the superficial dorsal vein, the dorsal artery, and the deep dorsal vein to Buck's fascia? The superficial dorsal vein lies superficial to Buck's fascia; the dorsal artery and deep dorsal vein lie deep to it.
3. How many dorsal arteries and deep dorsal veins are there? Two dorsal arteries and a single deep dorsal vein.
4. What is the arterial supply to the penis and the origin of each artery? The common penile artery (from the internal pudendal) gives the cavernosal, bulbourethral, and dorsal arteries.
5. Which artery is responsible for glans engorgement during erection? The dorsal artery.
6. What are the layers of the scrotum, and which abdominal layers contribute to the spermatic fasciae? Skin, dartos, external spermatic fascia, cremaster, internal spermatic fascia, tunica vaginalis, tunica albuginea, tunica vasculosa, testis. The external spermatic fascia comes from the external oblique, the cremaster from the internal oblique, and the internal spermatic fascia from the transversalis fascia.
7. Which defects comprise the Bell-Clapper deformity, and what innervates the anterior scrotum? Absence of the gubernaculum and posterior testicular fixation. The anterior scrotum is innervated by the ilioinguinal (L1) and the genital branch of the genitofemoral (L1–L2) nerves.